1. Field of the Invention
The present invention relates to a perpendicular magnetic recording head which is driven with a skew angle and performs a recording action by applying a recording magnetic field perpendicularly to a recording medium plane.
2. Related Background Art
As is well-known, a perpendicular magnetic recording head includes a main magnetic pole layer and a return yoke layer which have front end faces exposed at a surface opposing a recording medium (medium-opposing surface) and are magnetically coupled to each other on the deeper side of the medium-opposing surface in the height direction, a magnetic gap layer interposed between the main magnetic pole layer and return yoke layer on the medium-opposing surface, and a coil layer inducing a recording magnetic field between the main magnetic pole layer and return yoke layer upon energization. The recording magnetic field induced between the main magnetic pole layer and return yoke layer perpendicularly enters a hard magnetic film of the recording medium from the front end face of the main magnetic pole layer and returns to the front end face of the main magnetic pole layer through a soft magnetic film of the recording medium. This performs magnetic recording at a part opposing the front end face of the main magnetic pole layer. The size in the track width direction of the front end face of the main magnetic pole layer, i.e., recording track width size, has been becoming narrower as hard disk drives have been attaining higher recording densities.
In a perpendicular magnetic recording head having a narrowed track, how to suppress side fringing at the time of skewing where the head is driven in a state tilted with respect to a recording medium has become a problem.
As a method of suppressing side fringing at the time of skewing, it has conventionally been known to make a magnetic pole part of the main magnetic pole layer (the front end face exposed at the medium-opposing surface) attain a trapezoidal (bevel) form which is narrower on the leading edge side than on the trailing edge side when seen from the medium-opposing surface side. When the magnetic pole part of the main magnetic pole layer is narrower on the leading edge side than on the trailing edge side, magnetic fields leaking from side faces in the track width direction of the main magnetic pole layer at the time of skewing do not reach adjacent tracks on the recording medium whereby recording actions with less bleeding can be realized. The effect of suppressing side fringing becomes stronger as the bevel angle of the main magnetic pole layer is greater. However, the main magnetic pole layer with a narrowed track has a very small size in the track width direction. Therefore, when the bevel angle becomes greater, the main magnetic pole layer is shaved on the leading edge side, so as to exhibit an inverted triangular form, thereby failing to keep the size in the thickness direction. Since the main magnetic pole layer is formed by CMP (Chemical Mechanical Polishing) up to a position yielding a desirable thickness size after attaining a bevel form, fluctuations in the track width size due to CMP errors increases when the bevel angle becomes greater. Hence, it has not been possible for the main magnetic pole layer to attain a predetermined bevel angle or greater and fully suppress the side fringing.
Therefore, it has recently been proposed to provide the main magnetic pole layer with a magnetic shield layer as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 20055-92929), Patent document 2 (Japanese Patent Application Laid-Open No. 2005-190518) and Patent Document 3 (Japanese Patent Application Laid-Open No. 2005-310363).
Patent Document 4 (Japanese Patent Application Laid-Open No. 2005-174449) discloses a structure in which a magnetic bias film is formed on both sides in the track width direction of a soft magnetic film which is a part of a recording magnetic pole film.